1. Field of the Invention
The present invention relates to a battery pack in which a plurality of battery modules each having a plurality of cells are stacked with a gap therebetween, and in particular, to a battery pack in which a spacer for holding a battery module is placed between adjacent battery modules.
2. Description of the Related Art
In the related art, there is known a battery pack wherein a plurality of battery modules each having a plurality of cells are placed, and a spacer is placed between adjacent battery modules. The battery pack is, for example, a secondary battery (such as a nickel-metal hydride battery or a lithium ion battery) which is used as a power supply of an electric vehicle and a hybrid electric vehicle.
FIGS. 9-11 show a structure of a battery pack disclosed in WO 2006/087962 A1. FIG. 9 shows a structure of a holding spacer 130 which forms a part of the battery pack, FIG. 10 shows a structure of a battery module 110, and FIG. 11 shows a state of being assembled into a battery pack. A holding spacer 130 which holds the battery module 110 is placed between adjacent battery modules 110. The battery module 110 and the holding spacer 130 are overall constrained by two end plates (end boards) 180 and four constraining rods 185, to become an integrated structure. In addition, the battery module 110 and the holding spacer 130 are held by a first spacer support member (upper case) 160 and a second spacer support member (lower case) 170. The first spacer support member 160 and the second spacer support member 170 are fixed by a bolt 173 and a nut 175.
Each battery module 110 has an approximate rectangular parallelepiped shape including two opposing long side surfaces 110a and 110b, two opposing short side surfaces 110c and 110d, and two opposing end surfaces 110e and 110f. The battery module 110 comprises a plurality (in the figures, eight) of cells 111 which are placed in one line. The cells 111 are connected in series with a safety valve facing toward a side of the short side surface 110c. An upper cover member 113 which covers each safety surface and which forms a gas discharge path with the cell case is placed on the side of the short side surface 110c of the cells 111 connected in series. In addition, a negative electrode side cover member 115 is placed on the side of the end surface 110e of the placed cell 111, and a positive electrode side cover member 117 is placed on the side of the end surface 110f. An external negative electrode terminal 116 which protrudes to the outside of the module is provided at an approximate center of the negative electrode side cover member 115, and an external positive electrode terminal 118 which protrudes to the outside of the module is provided at an approximate center of the positive electrode side cover member 117. A discharge hole 119 is provided at an upper section of the positive electrode side cover member 117, which is in communication with the gas discharge path formed between the upper cover member 113 and the cell cases.
The holding spacer 130 is placed between the battery modules 110 to hold the battery module 110, and forms, between the battery module 110 and the holding spacer 130, a cooling path through which a coolant is circulated. The holding spacer 130 comprises a spacer body 131 having an approximate plate shape and which is directly interposed between the battery modules 110. In the spacer body 131, a plurality of first module support sections 133 which support the short side surfaces 110c of the adjacent battery modules 110 are provided on an end in a vertical direction Z. In addition, in the spacer body 131, a plurality of second module support sections 135 which support the short side surface 110d of the adjacent battery modules 110 are provided on the other end in the vertical direction Z. The battery module 110 which is mounted on the holding spacer 130 is placed between the first module support section 133 and the second module support section 135, so that movement in the vertical direction Z is restricted. Moreover, in the spacer body 131, a plurality of third module support sections 137 which support the end surface 110e or 110f of the battery modules 110 that are placed adjacent to each other are provided on one end in a direction of placement X of the cells. In addition, in the spacer body 131, a plurality of fourth module support sections 139 which support the end surface 110e or 110f of the battery modules that are placed adjacent to each other are provided on the other end in the direction of placement X of the cells. The battery module 110 mounted on the holding spacer 130 is placed between the third module support section 137 and the fourth module support section 139, so that movement in the direction of placement X of the cells is restricted. Moreover, in the spacer body 131, a plurality of cooling path forming projections 141 are provided in order to form a cooling path for circulating coolant between long side surfaces 110a and 110b of adjacent battery modules 110. The cooling path forming projection 141 projects in a direction of placement Y of the module and extends in a straight line shape in the vertical direction Z. The long side surfaces 110a and 110b of the battery module 110 mounted on the holding spacer 130 contact the cooling path forming projections 141, to form the coolant path between the long side surfaces 110a and 110b and the spacer body 131. A first elastic member 143 and a second elastic member 145 are formed with rubber, and prevent free movement of the holding spacer 130. A plate-shaped rubber member 147 is held on the holding spacer 130 in a state where the rubber member 147 is elastically deformed in the direction of placement Y of the module and elastically contacts the long side surface 110a or 110b of the battery module 110. With this structure, the battery module 110 is elastically held by the holding spacer 130.
On the other hand, when the temperature is low, the output of the battery pack is reduced and sufficient performance cannot be achieved. In consideration of this, a technique has been proposed in which the battery pack is heated when the automobile is run under a very cold environment. For example, JP 2003-223938 A discloses a battery device in which a plurality of secondary batteries are heated by a sheet-shaped heat generating structure which uniformly generates heat over the entire surface.
Although provision of the sheet-shaped heat generating structure which uniformly generates heat over the entire surface is effective when the battery pack is to be heated in a cold climate, with a structure of simply adding the heat generating structure, the number of components is increased and the structure becomes more complex. Therefore, a structure is desired to reliably heat the battery pack in the cold climate and to achieve superior performance of the battery pack while maintaining the already-existing structure of the battery pack as much as possible.